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wuddup guys, just messed up my car while installing my headunit. So far I am not receiving power to my head unit nor is my alarm working. At first i thought it was my radio fuse because it was blown, but after i replaced it, i was still was not getting any power to my hu. I believe i shorted the multiplex control unit under the dash/fuse box. I searched on these forums, but i cant seem to find where the control unit is located. Any help or advice would be much appreciated. Thanks

problem list
not receiving power to head unit
door locks won't work unless key is in the ignition
car alarm will not activate.

Good stuff, let's have you meter both sides of that BackUp fuse so we can figure out whether the problem is before or after the fuse.

Quote:

Originally Posted by AnaRki

But as for the MCU, if i need to replace it do i have to go to the dealership?

As per electric130, sounds nasty. To be honest I would be surprised if that ended up being what you needed to do to fix the problem. Whether or not power is getting to the BackUp fuse will tell us a lot though.

I just had a very similar problem with my '01 Civic. I also had trouble installing my head unit....shorted the +12V power to the radio to ground. I then checked quite a few fuses (finding none to be at fault). The radio didn't work, plus the power locks, dome light, and the don't-leave-your-headlights-on chime were also out of commission when the key was not in ACC position. My troubleshooting via the Haynes manual led me to believe the Multiplex Control Unit was at fault. I had poked around the interior fuse panel for a while before giving this forum a look, to see if anyone could point me to how to troubleshoot that MCU.

It turned out to be the "Back Up" fuse that was blown. My thanks and appreciation to this thread for saving me any more headaches trying to solve this problem.

I think I found it. I changed the fuse box (30 min)and all seems to be working good. I had some issues from ebay so after some wrong ones and some 3 weeks later I ended up with 3 fuse boxes. But it seems to fixed it. I think is was the multiplex control unit that is in the fuse box. I looked at all the wiring diagram's and it all made since. All the grounds for the issues I had went to the Multiplex unit. Best bet is the link above at honda parts its around 150$ shipped And you won't have to deal with ebay. Dealer is 136.00 or 160. at customer cost if they even have it (my dealer didn't) My car the a/c, door locks,Key - in reminder,intermittent wiper Did not work and the ebrake light stayed on. Hope this helps the next person.

I have a simmillar prob wiz my civic (02 EXi).My keyless, a/c, dom light, intemittent wiper, reminders, seat belt & trunk light stop working at the same time. Only the parking brake light stayed on.I did a diagnostic but cannot connect to the MCU.If the Multiplex Control Unit must be replace, can anyone tell me if the key must be re programmed?Thanks

I have an 05 civic ex that i think i need to change the multiplex/interior fuse box. can someone point me to a diagram that will show me what i need to do to access this thing? Any help would be greatly appreciated.

So obviously this isn't a new issue, is there any kind of recall on the MCU? I saw a few TSB's on it but I was never able to access the exact information. Just bought my 02 civic ex with all of the above mentioned problems and thanks to multiple threads discovered the cause of all the issues. At least it's only one thing to fix instead of 9 or 10!! Any help as far as alternate places to get a MCU would be of great help too!!

4. Fuse box is under central portion of dash. Locate and disconnect all connectors on the side facing you.

5. Disconnect this bolt:

6. Slide fuse box down out of bracket

7. Disconnect all connectors on the back side

8. Do it all in reverse

*NOTE: The SRS connectors (always yellow, you can't miss 'em) have a spring loaded sleeve. To disconnect: pull on the sleeve (not the connector). To reconnect: push on the connector (not the sleeve)

I just used the SRS connector on the side of the steering column as an example. You can see the under-dash fuse box in the left side of the frame. My finger is on the sleeve portion that I'm talking about:

My car also seem to have similar problem! I lost one Power Window and Central Locking, along with AC. Can you provide me the link where you bought the MCU? I couldn't find any link in the thread. Appreciate your quick help.

Thanks,
Safuvan
------------

Quote:

Originally Posted by bigmacnfrys

I think I found it. I changed the fuse box (30 min)and all seems to be working good. I had some issues from ebay so after some wrong ones and some 3 weeks later I ended up with 3 fuse boxes. But it seems to fixed it. I think is was the multiplex control unit that is in the fuse box. I looked at all the wiring diagram's and it all made since. All the grounds for the issues I had went to the Multiplex unit. Best bet is the link above at honda parts its around 150$ shipped And you won't have to deal with ebay. Dealer is 136.00 or 160. at customer cost if they even have it (my dealer didn't) My car the a/c, door locks,Key - in reminder,intermittent wiper Did not work and the ebrake light stayed on. Hope this helps the next person.

I seem to have a MCU problem also, but when checking the fuses in the "under dash" fuse box, my "check engine" alert appeared. Does anyone help me understand how to clear it. Thank you, Wes

I just replaced mine today because I was as well having electrical issues myself.
FIRST- The fuse box under the dash is the problem. There are letters where each harness plugs into. Label them as you pull them out because there is alot.
SECOND- You need to have the new fuse box ready to plug into the new one.
CAUTION!- If they send you one for a two door and you have a four door (which is what happened to me) all you have to do is open up the two fuse boxes (starting from the top and working down works great) switch the electronic board that is on the top (or what some have been refering to as the "multiplex control unit") then assemble it back together.
THIRD- Plug the harnesses back into the appropriate slots and mount back under the dash.

just replaced my fuse box on my 05 civic. took it for a spin and everything seemed to be fixed. I got back in the car a few hours later and the problems are back all of a sudden. Is there anything that could be causing the mcu to go bad?

I have an 01 Civic EX - same problem as other posts happened Today ironically, Dome light does not light while door is Open, Power locks don't respond to remote or door switch, A/C does not cool, and Brake light stays lit on dash.....

All forums/threads point to MCU under steering column,
Honda Part**** 38200-S5A-A31, about $150 bucks online from Honda parts now. Will let you know what happens when I replace it.

Old post, but im going to bump it. I was an idiot and did not disconnect battery with new cd player install. Went to turn it on, typical MCU issues, no locks, no dome lights, no stereo, no chimes. Backup fuse was fine. Ordered a new fuse box, matched it to my VIN $240. Checked all of my connections with wire harness. Everything is secure and matched up. Installed new fuse box today. When i reconnected the battery i had a good spark when attaching the negative. Get in the car. Same issues as before. I'm about to have a mental breakdown with this. I've only owned the car for a week!

Any ideas out there? Should I ground the cd player to the metal frame instead of into the harness? That seems to to be the only variable that has changed from the wiring of the factory cd player. The new cd player was directly out of my accord which had zero electronic problems.

Please help! I'm a grown man and almost cried today when it didn't work! ahha

Just checked. All large fuse block are still intact. When I plugged in the new fuse panel, i had the aftermarket cd player installed. Wiring seemed fine. I there a special way that I need to wire in the aftermarket cd player?

Strange thing is, that I only have a few signs of a bad MCU.
My power locks do not work
Reminder does not work
Radio does not work
Dome light upon door entry does not work
Dome light works with key in the on position and doors open

Things that differ from most posts.
A/C does work great
Intermittent wipers work
E-brake light is NOT on
Airbag light IS on
Auto locks do not work with key in on position

I just tested every single fuse in the car with a test light. Each side of the fuse works properly.

Something isn't adding up. I'm still baffled. Is it time to go to a shop?

..... waiting on an email reply from craigW. I also noticed today that my tripometer resets itself each time i start the car. It seems that all of these have a common power source/ or common ground that is not functioning?

Thanks everyone for your help on this! I can post pictures of stereo wiring if that helps.